Grand Parents siblings.
My Great Granduncle
They would be your grandparents brother of sister
granduncle - grandnephews/grandnieces
the second hokage was Tsunade's granduncle
keke palmer is my cousin her grandpa is my granduncle
You would be their great-granduncle or great grand aunt, and they are your great-great nieces or great-great nephews.
You are the nephew if you are male and a niece if you are female.
Your grandmother's brother is your children's great-granduncle (or great great uncle). They are his great-grandnieces and great-grandnephews.
just the first and second are brothers but the rest are not
Bullroarer was huge for a hobbit--he could ride a horse. Bullroarer was the great-granduncle of Old Took, which was Bilbo's grandfather.
Your great grand unlce's great grandniece could be you (if you are a girl), any of your sisters, or some of your first cousins or second cousins or third cousins who are girls.
Your father's uncle is commonly referred to as your great-uncle or granduncle. Alternatively, you can also call him simply "uncle," but specifying "great-uncle" provides clarity about the family relationship.